The subject matter disclosed herein relates to fire extinguishing agents and systems. More specifically, the subject disclosure relates to the mixing and dispensing of fire extinguishing agents and propelling gas.
Total-flooding fire-extinguishing systems (FXS) are used to extinguish fires in enclosed protected spaces by creating fire-extinguishing atmospheres therein. A fire-extinguishing atmosphere (FXA) is created by adding a gaseous fire-extinguishant (GFX), also referred to as a gaseous fire-extinguishing agent, to the air in the protected space in sufficient quantity to exceed the minimum extinguishing concentration (MEC) of the GFX for the type of fuel that is burning. Gaseous fire-extinguishants comprise either ordinary gases such as nitrogen, argon, carbon dioxide, and other non-oxidizing gases, or of vaporizing liquids or liquefied compressed gases usually including of one or more chemicals based on carbon and fluorine chemistry such as hydrofluorocarbons, fluoroketones, perfluoroketones, perfluorocarbons, fluoro-olefins, and similar chemicals including those whose chemical structure contains chlorine and bromine. Where a GFX comprises one or more ordinary non-liquefied gases, the agent container is filled uniformly with compressed GFX gas. Where a GFX consists of a liquid or a liquefied compressed gas, the agent container is only partially filled uniformly with GFX leaving an ullage space above the liquid to accommodate pressurized expellant gas. Prior to delivery of the GFX to the protected space the GFX is stored in one or more containers that are either pressurized with an expellant gas or gas mixture which typically includes the gas or vapor of the agent itself plus, as required, additional expellant gas such as nitrogen, argon, carbon dioxide or other pressurized gas. The GFX storage container may be pre-pressurized or pressurized at the time the FXS is called upon to operate to deliver GFX to the protected space. Elements of the FXS necessary to deliver the GFX to the protected space include the GFX storage container and its subcomponents, including a discharge valve; a pipe system, which may be branched, through which the GFX flows from the location of the storage container to one or more points of discharge in the protected space; and a nozzle at each point of discharge to disperse the GFX into the atmosphere of the protected space.
An important measure of performance of a FXS is the maximum delivery length of the pipe system through which the GFX can be conveyed while maintaining at each nozzle a sufficient pressure to assure effective dispersion of the GFX into the protected space. The maximum delivery length in an FXS where the source of propellant gas comprises only that propellant gas contained in a pre-pressurized storage container is relatively limited owing to the reduction of pressure in the storage container during the course of expelling the GFX. In order to project agent through longer pipe systems, more propellant energy, or pressure, is required at the agent container. This can be achieved by simply increasing the amount of propellant gas, usually nitrogen, initially charged to the pre-pressurized agent container, but this approach is limited by the working pressure of the container. In the case of a pre-pressurized GFX container, where the GFX is a liquid or liquefied compressed gas, a portion of the propellant gas added to the ullage space to pre-pressurize the agent container, usually nitrogen, becomes dissolved in the liquid phase at a saturation concentration related to the pressure and temperature of the container.
Another approach, where the GFX is a liquid or liquefied compressed gas, is to add propellant gas to the ullage space of an unpressurized agent container, except to the extent that the container is pressurized by the vapor pressure of the GFX contained therein, just before the need to dispense the agent from the container, specifically adding the propellant to the ullage space in the container above the agent liquid. The approach of adding propellant gas to the ullage space in a GFX container at the time of operation is sometimes referred to as the “piston-flow” approach, because the additional pressure energy contributed by the added propellant acts as a “piston” to force agent liquid into the pipe system via a siphon tube with an entrance near the bottom of the container. The piston-flow approach, when applied to a non-pre-pressurized GFX container delivers an agent free of nitrogen to the nozzle.
The approach described above may also be used to add additional propellant gas to a pre-pressurized container for the purpose of maintaining high pressure in the container during the discharge period